It is common to provide spring or air cushion devices which operate to open or close doors, but there are situations where a door is subjected to pressures which make opening the door by hand very difficult or impossible. One such situation is the fire escape stairwell which is commonly contructed in multi-story buildings. Such stairwells extend between floors of the building and have doors to each of the floors. A main function of such stairwells is to provide an escape for occupants on a floor in the event of a fire, and at the same time prevent the spreading of a fire between floors.
More recently it has been the practice to provide an air blower which in the event of a fire alarm will create a pressure in the chamber defined by the stairwell so that when the door to the stairwell is opened on any floor on which there is a fire the draft will be from the interior toward the exterior of the chamber rather than from the floor into the stairwell. The effect of this is to keep the fire from entering the stairwell and passing to other floors.
One difficulty with such an arrangement is that the pressure generated by the blower is applied to the inside of the door and it is difficult or impossible to move the door by hand about its hinges into the stairwell to open the door. Further, it is necessary that the door be opened and closed normally in the absence of any fire alarm.
I have set myself to the problem presented by a situation such as that above described and have devised apparatus and methods which will assist in the opening of the door when the pressure is applied but which will allow the normal opening and closing of the door without interference when the pressure is not being applied.